Abstract: It was found that the second pass of a power-wheel would encounter less moving resistance and obtain higher efficiency. This led to the broad use of 4WD tractors and the tendency of using them instead of crawlers. In paddy field, the 4WD boat tractors were also proved to have excellent tractive efficiency and performance, with their power-wheel lug stepping along the previous cavities in ruts. A special experimental research was conducted on the dynamic performance of 4WD paddy tractor with its power-wheel lugs stepping along the previous cavities in ruts. A 3-lug model wheel of original size with sensors was designed to simulate this working condition. The optimum distance between the previous cavity of front-wheel-lug and the following cavity of rear-wheel-lug, the rate of cavity displacement, the lug pull and lift force, the lug efficiency and the influencing factors (slip, inclined angle, depth and number of lug) on performance were analysed and studied based on experiments in this paper.